Design for electrostatic generator/motor electrodes located on the inner surface of an electromechanical battery rotor

ABSTRACT

A geometric design of E-S generator motor electrodes mounted on the inner surface of a fiber-composite rotor is provided. The electrode configuration is able to sustain very high g levels. The rotor may be funned of carbon-fiber wound on top of an inner E car S-glass fiber composite core. The electrode design provides the needed area to satisfy the power requirements of the storage system and utilizes a stacked wedge-like electrode array that both solves the high-g problem and results in a doubling or tripling of the electrode area, relative to that of electrodes that conform to the inner cylindrical surface of the rotor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 15/076,472titled “Improved Design for Electrostatic Generator/Motor ElectrodesLocated on the Inner Surface of an Electromechanical Battery Rotor,”filed Mar. 21, 2016, incorporated herein by reference. U.S. patentapplication Ser. No. 15/076,472 claims the benefit of U.S. ProvisionalPatent Application No. 62/207,341 titled “Improved Design forElectrostatic Generator/Motor Electrodes Located on the Inner Surface ofan EMB Rotor,” filed Aug. 19, 2015, incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No, DE-AC52-07NA27344 between the U.S. Department of Energy andLawrence Livermore National Security, LLC, for the operation of LawrenceLivermore National Laboratory.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to electromechanical battery (EMB)electrode design, and more specifically, it relates to means forovercoming the high g load on the rotor electrodes of an EMB.

Description of Related Art

In the design of EMB flywheel energy storage modules utilizinghigh-strength fiber composite rotors and electrostatic generator/motors,the electrodes of such modules must withstand very high centrifugalforces. This situation is particularly evident for small rotors (e.g.,diameters of 10 cm or less) that may operate at speeds in excess of200,000 RPM. In such modules, the centrifugal force at the inner surfaceof the rotor may be of in excess of a million g, implying that an itemweighing only 1 gram on the inner surface of the rotor will have anequivalent weight of over 1 metric ton. Since even the lightestelectrode structure for the rotor can be expected to weigh tens ofgrams, its equivalent “weight” can be of order 10 to 100 metric tons.This centrifugal force will be exerted on the inner surface of therotor. A simple and practical solution to this high-g load problem isdesirable. A means of increasing the rotor electrode area by asubstantial factor relative to the area of the inner surface of therotor is also desired since increasing the electrode area of an E-Sgenerator results in a proportionate increase in power output from thegenerator.

SUMMARY OF THE INVENTION

This invention pertains to the geometric design of E-S generator/motorelectrodes mounted on the inner surface of a fiber-composite rotor.Particularly in small EMB rotors, the centrifugal g-forces are very highso that the E-S rotor electrode design must be such as to be able tosustain these forces. In addition, if the rotor is fabricated fromcarbon-fiber composite, its electrical conductivity would interfere withthe proper operation of the E-S generator/motor electrodes. Sincecarbon-fiber rotors are commonly wound on top of an inner E or S-glassfiber composite core, mounting the electrodes on the inner surface bothcan solve the high-g problem and the carbon-fiber conductivity problem.The issue then is to achieve the needed area to satisfy the powerrequirements of the storage system. This problem is most evident invehicular applications. This invention pertains to a design that employsa stacked wedge-like electrode array that both solves the high-g problemand results in a doubling or tripling of the electrode area, relative tothat of electrodes that conform to the inner cylindrical surface of therotor. The invention can be used in flywheel storage systems or otherrotating machinery, including for vehicular or stationary use.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, illustrate embodiments of the invention and, togetherwith the description, serve to explain the principles of the invention.

FIG. 1A is a schematic section drawing of an EMB rotor comprising acarbon fiber wound on top of an inner E- or S-glass fiber composite corewith rotor electrode support rings on the inside surface of the rotor.

FIG. 1B is a schematic section drawing of an electrically non-conductingEMB rotor with rotor electrode support rings on the inside surface ofthe rotor.

FIG. 1C is a schematic section drawing of an EMB rotor comprising acarbon fiber wound on top of an inner E- or S-glass fiber compositecore, where the inner core has been machined to form slots.

FIG. 1D is a schematic section drawing of an electrically non-conductingEMB rotor where its inner surface has been machined to form slots.

FIG. 2 is a schematic section drawing of a stator electrode end.

FIG. 3A shows a rotor section of FIG. 1 and shows an upper statorsection and a lower stator section where each stator includes arrays ofthe electrodes of FIG. 2.

FIG. 3B shows an axial view of the stator of FIG. 3A

DETAILED DESCRIPTION OF THE INVENTION

In the design of the fiber-composite rotors for EMBs, high-strengthfibers are embedded in an epoxy matrix. The fibers used include E-glassand the higher-strength S-Glass, basalt fibers, and carbon fibers suchas IMS65 and the highest strength carbon fiber, T1000 (tensile strength7 Gpa, i.e., about 1 million psi). In the context of this invention, itis important to note two circumstances. First, it should be noted thatcarbon fiber composites are electrically conducting and this fact mustbe considered when designing the electrode system for an E-Sgenerator/motor to be mounted on the rotor. The second circumstancerelates to a rotor design practice that is commonly employed whendesigning and constructing carbon-fiber composite rotors. That is, infilament winding of the rotor, the innermost composite layers are madeusing S-glass instead of carbon fiber. This two-layer design is employedbecause carbon-fiber composites are highly sensitive to the presence ofpoint loads, while S-Glass composites are much less sensitive.Centrifugal stresses within the S-glass composite are transferred inpart to the high-modulus carbon-fiber composite so that the S-glass isnot stressed above its safe working limit.

The first circumstance implies that when the outer part of the rotorbody is composed of carbon-fiber composite, its electrical conductivityprecludes the location of the conducting strips required for theelectrodes on the outer surface of the rotor. In such a case, theconductivity of that part of the rotor surface lying between the stripswould greatly vitiate the performance of the E-S generator. Thus, forcarbon fiber composite rotors to be made compatible with the use ofsurface-mounted rotor electrodes, these electrodes must be located onthe inner surface of the rotor, and that inner part of the rotor must benon-conducting, i.e., it must be composed of glass or basalt fibercomposite.

The next issue faced by the designer is to insure that the electrodearea is sufficiently large to generate the power required by theapplication. If the application of the EMB is the bulk storage ofenergy, with hours-long charging and discharging times, then simpledesigns can be used. An example would be to use vertical strips of metalfoil or metallic coating on the inner surface of the rotor. However, ifthe peak power demands are substantially higher, as they would be invehicular applications, for example, then a higher electrode area wouldlikely be required. The invention thus addresses two issues: (1) Dealingwith high-g centrifugal force fields, and (2) Increasing the electricalcapacitance and the max/min capacity ratio of the E-S electrode system.

The basic concept of the new system is illustrated schematically in thesection views shown in FIGS. 1 and 2.

FIG. 1A shows a sectional view of hollow cylindrical rotor 10, which isformed of a non-conducting core 12 within a carbon fiber composite 14.The inner surface of the rotor 10 has been configured to includemultiple vertically spaced cells 16, bounded on their upper and lowersurfaces by wedge-shaped fiber-composite separator rings 18. Oneexemplary embodiment of the rings is formed of G-10 glass and another isformed of fiberglass. Other embodiments are possible. Thus, aconfiguration of cells is achieved by assembling a stack offiber-composite rings of the proper shape within the inside surface ofthe glass or basalt fiber-composite inner portion of the rotor. In thisembodiment, the separators are made wedge-shaped instead of beingconstructed as constant-thickness discs in order to minimize thecompressive stresses that will occur at their bases; however, othershapes are within the scope of the invention. Note that is can bebeneficial to make the tips of the rings 18 to be rounded rather thanpoints pointed tips tend to have a lower breakdown voltage. Likewise,the troughs of the cells can benefit from having rounded corners ratherthan sharp corners. This same principle applies to all of the electrodeconfigurations described herein. Keeping these stresses within theirlimiting value will also determine the maximum value of the ratio of theouter radius of these rings to their inner radius. FIG. 1B is asectional view that shows a configuration where rotor 11 is conductiveand where the inner non-conducting core of FIG. 1A is omitted.

An alternate configuration of cells can be achieved by machining slotson the inner surface of the rotor as shown in the sectional view of FIG.1C. In this configuration, the inner surface is machined in anelectrically non-conducting core 20 around which is wound a carbon fibercomposite 22. Note that the core 20 can beneficially have all rounded orbeveled corners to increase the electrical breakdown voltage. FIG. 1D isa sectional view that shows another rotor configuration having slotsmachined on the inner surface. In this embodiment, the entire rotor 30is formed of electrically non-conducting material. Note that the core 20can beneficially have all rounded or beveled corners to increase theelectrical breakdown voltage. As much as possible, the contour of thepeaks and troughs should be uniform.

FIG. 2 shows a side sectional view of a “blade” 40 of the stator. Toachieve a high max/min capacity ratio and also to enhance thevoltage-holding ability of the electrode system, a tapered cross-sectionmetal electrode 42 is employed. This electrode is then completelysheathed by a high dielectric constant polymer 44, e.g., polyester fibercomposite (K=10 at E-S generator frequencies). The max/min ratio farthis electrode structure depends upon the structure geometric parametersbut can be expected to be 3:1 or greater. Although the figure shows theblade as having corners, it is beneficial if the edges that face therotor electrodes are rounded or beveled. It is beneficial to have arounded top, rather than a flat top.

The new conductor array is can be incorporated into a “balanced circuit”system (See FIG. 15 in U.S. Pat. No. 7,834,513, incorporated herein byreference). In using this circuit, the rotor electrodes operate in a“virtual ground” situation. That is, the stator is divided into an upper(“plus” charged) section and a lower (“minus” charged) section. See FIG.3A, described below. The E-S generator capacitor is thus divided into anupper and lower half, with the rotor electrodes, which run the fulllength of the rotor, completing the circuit. These electrodes could bemade, for example, of vertical strips of metal foil bonded to the innercorrugated surface of the rotor cell structure. Their positioning wouldbe such as to match the periodicity of the stator electrode system, byincorporating an azimuthal gap between them with the same periodicity.To optimize the max/min capacity ratio, the gaps between the rotorconductor strips might be made wider than the width of the stripsthemselves.

More specifically, FIG. 3A shows a sectional view of one side of therotor 50 which includes the separator rings 52 on which is laid down aconducting strip 53. In this embodiment, the rotor is electricallynon-conductive. The figure also shows an upper series of statorelectrode blades 54 and a lower series of stator electrode blades 56.The upper series of blades 54 are in electrical contact with conductivestrip 58, which is attached to stator section 60. The lower series ofblades 56 are in electrical contact with conductive strip 62, which isattached to stator section 64. Notice the gap 66 between stator section60 and stator section 64. If the upper and lower stator sections areformed of electrically conductive material, the conductive blades 54, 56can be in direct contact with stator sections 60, 64 and conductivestrips 58 and 62 can be omitted. Although the conducting strip 53 isshown as having a pointed peak, it is beneficial if the peak is rounded.Likewise, although the blades 54 and 56 are shown as having flat tops,it is beneficial if they are rounded. Although the blades appear to havenon-uniform sizes and dimensions, it is beneficial if they all are asidentical as possible. FIG. 3B shows an axial view of the stator of FIG.3A and shows rotor 60, strip 58 and blades 54. For clarity, a balancedcircuit similar to the one shown in FIG. 15 of U.S. Pat. No. 7,834,513is provided. A source 80 of positive voltage is connected to inductor 82and resistor 84 and to conductive strip 58. A source 86 of negativevoltage is connected to inductor 88 and resistor 90 and to conductivestrip 62. Note that it is beneficial if the conducting strip 53 is aplating rather than a foil. Such plating can be formed vapor deposition.In this embodiment, a connection is made from a node 85 between resister84 and strip 58 to a node 91 between resistor 90 and strip 62. Theconnection from node 85 is made to a capacitor 94 and to a load 96 to acapacitor 98 to node 91. Based on the teachings herein, those skilled inthe art will understand that other circuits are useable with theconfiguration of FIG. 3A. Assembly of this and similar embodiments canbe accomplished by building or stacking the device from one end of therotor. For example, starting at the bottom of the rotor 50 withreference to the page, a first ring can be attached to the rotor. Then,a blade is attached to the stator. The assembly process is continued upthe rotor. They rotor electrode cart be deposited by rotating the rotorsuch that is does not directly line up with the stator electrodes. It ispossible to first fabricate the stator and its blades and then connectthe rotor sections around the stator. Similarly, the rotor can beprefabricated and the stator assemble inserted in sections within theinner radius of the cylindrical rotor. Other assembly procedures will beapparent to those skilled in the art based on this disclosure. It isalso possible to make the rotor blades to be rings with non-conductingmaterial located along the longitudinal axis of the stator on itsoutside wall such that there are conducting blades corresponding to thespacing of the rotor electrodes.

EXAMPLE CALCULATIONS

To demonstrate aspects of the performance of the new electrode geometry,a calculation of the ratio of the capacitor area with the newconfiguration located on the inner surface of a rotor with a given innerradius to that for electrodes mounted indirectly on that inner surface.The number of cells of the example was that shown in FIG. 1A. For thiscase the area ratio was 25:1. Higher values could be obtained, if needbe, by increasing the number of cells. In addition, a calculation wasmade of the compressive stress at the base of the wedges in a smallrotor with an inside radius of 0.035 m., operated at 250,000 rpm. Thecalculated stress was 293 MPa, well below the maximum compressive stressvalue cited in the literature for glass-fiber composite (e.g., G-10fiber-glass composite, 448 MPa).

Thus, a new electrode configuration has been described, one designed forinstallation on the inside of the rotor of an EMB, and aimed at the twinobjectives of operation at high centrifugal g levels at the same timeincreasing the electrode array as needed, for example, in vehicularapplications. The results of calculations showing the improvedperformance were also given.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The embodiments disclosed were meant only to explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best use the invention in variousembodiments and with various modifications suited to the particular usecontemplated. The scope of the invention is to be defined by thefollowing claims.

We claim:
 1. A method, comprising: providing an open cylindrical rotorhaving an inner wall and a longitudinal axis of rotation (AOR), whereinsaid inner wall comprises a rotor electrode mounting surface, whereinthe distance from said AOR to said mounting surface periodically variesalong the length of said AOR, wherein said surface comprises a series ofrings attached to said inner wall, wherein said rings are oriented to beperpendicular to said AOR, wherein each ring of said series of rings hasa base and a peak, wherein said base is connected to said inner wall,wherein said peak points toward said AOR, wherein said base is widerthan said peak, wherein said rotor comprises fibers embedded in an epoxymatrix, wherein said fibers comprise a material selected from the groupconsisting of E-glass, S-Glass, basalt fibers and carbon fibers andwherein said inner wall is electrically non-conductive; providing rotorelectrodes fixedly attached to said mounting surface, wherein said rotorelectrodes have a long dimension that is oriented in the direction ofsaid AOR; providing a stator located within the hollow portion of saidopen cylindrical rotor, wherein said stator comprises an outer surface;providing stator electrode blades attached to said outer surface,wherein said blades extend radially outward from said outer surface andare periodically spaced azimuthally in rows and columns around saidouter surface, wherein as said rotor rotates, said rings areunobstructed by said blades; and rotating said rotor.
 2. The method ofclaim 1, wherein said peak is rounded or beveled.
 3. The method of claim1, wherein each ring of said series of rings comprises material selectedfrom the group consisting of G-10 glass and fiberglass.
 4. The method ofclaim 1, wherein said carbon fiber composite is wound onto anon-conducting core that includes said inner wall.
 5. The method ofclaim 4, wherein said non-conducting core comprises a material selectedfrom the group consisting of glass and basalt fiber.
 6. The method ofclaim 1, wherein said rotor electrodes comprise strips of metal foil. 7.The method of claim 1, wherein said rotor electrodes comprise metalliccoating.
 8. The method of claim 1, wherein said rotor comprises multiplespaced cells in the direction of said AOR, wherein said cells arebounded on their upper and lower surfaces by said rings.
 9. The methodof claim 1, wherein said rings are wedge-shaped.
 10. The method of claim1, wherein said mounting surface comprises slots in said inner wall. 11.The method of claim 1, wherein each blade of said blades comprises anelectrically conductive portion that is sheathed with dielectricmaterial, except for the portion of said blade that is in electricalcontact with said outer surface.
 12. The method of claim 11, wherein theedges of said blade that face said rotor electrodes are rounded orbeveled.
 13. The method of claim 11, wherein azimuthally, thepositioning of said blades matches the periodicity of said statorelectrodes
 14. The method of claim 1, wherein the gaps between saidrotor electrodes are wider than the width of a rotor electrode.